If the berries are full of tough seeds, remove seeds by forcing berries through a food mill or a mesh sieve into a large bowl. If berries are mostly seed less. Place them in a large bowl. Stir in sugar, and let stand at room temperature. For 30 minutes. In the work bowl of a food processor fitted with the medal blade, puree berry mixture. Pour into a large glass or metal bowl.

Whisk in buttermilk. Cover, and refrigerate until mixture is very cold (40 degre or lower), at least 4 hours, then atir well. Freeze sherbet in a gel type ice cream freeze according to the manufacturer’s instructions. The sherbet will be soft, like a thick milk shake. To freeze hard enough to scoop, transfer to an airtight container, press plastic wrap directly onto the surface, and freeze until firm. Garnish with fresh blackberries, if desired.